Photographic production of phase holograms and developing with a nontanning developer

ABSTRACT

Photographic process for the production of phase holograms in silver halide emulsion layers. After exposure to light reflected from the hologram structure, the silver halide emulsion layer is developed with a nontanning developer, treated with a short stop bath, washed and then bleached in an oxidizing bleaching bath. The silver compound produced in the exposed areas of the layer by the bleaching process is dissolved out and the layer is then dried. Suitable non-tanning developers are, in particular, hydroquinone, 1-phenyl-pyrazolidone-3 or a compound or the paminophenol series.

United States Patent [191 Eggers et al.

1 June 11, 1974 [75] Inventors: Joachim Eggers; Hans-Theo Duschmann, both of Cologne, Germany [73] Assignee: AGFA-Gevaert Aktiengesellschaft,

Leverkusen, Germany [22] Filed: Apr. 26, 1972 [21] Appl. No.: 247,812

[30] Foreign Application Priority Data Apr. 28. 1971 Germany 2120864 [52] US. Cl 96/27 H, 96/62, 96/60 BF [51] Int. Cl G03c 5/04 [58] Field of Search 96/27 H, 60, 62

pages 713-719.

Applied Optics, Shankoff, Oct. 1968, Vol. 7, No. 10, pages 2101-2105.

Primary ExaminerR0nald H. Smith Y Assistant Examiner-John L. Goodrow Attorney, Agent, or Firm-Connolly and Hutz [57] ABSTRACT Photographic process for the production of phase holograms in silver halide emulsion layersv After exposure to light reflected from the hologram structure, the silver halide emulsion layer is developed with a nontanning developer, treated with a short stop bath, washed and then bleached in an oxidizing bleaching bath. The silver compound produced in the exposed areas of the layer by the bleaching process is dissolved out and the layer is then dried. Suitable non-tanning developers are, in particular, hydroquinone, l-phenylpyraz0lidone-3 or a compound or the p-aminophenol series.

5 Claims, No Drawings PHOTOGRAPHIC PRODUCTION OF PHASE HOLOGRAMS AND DEVELOPING WITH A NONTANNING DEVELOPER The invention relates to a process for the production of low noise, high light intensity phase holograms in photographic layers, using the desensitized residual silver halide for constructing the hologram.

It is known that phase holograms have substantially higher image brightnesses than amplitude holograms. Since the photographic silver halide emulsion layers used in holography are much more sensitive than other systems such as polymer layers which can be crosslinked by light or chromate-gelatin layers, attempts have been made to produce phase holograms in such silver halide gelatin layers by reconverting the silver obtained after development into a silver salt by a bleaching process. As a rule, such bleaching processes substantially reduce the contrasts in holographic reconstructions so that the quality ofthe imageobtained is unsatisfactory. Chemical development of exposed silver halide gelatin layers converts each silver halide grain into an elongated, usually curved thread of metallic silver the longitudinal dimension of which is greater than the diameter of the original silver halide grain. The bleaching process causes this silver thread to become coarser so that centres of scattering which are effective over a larger cross-section are produced, with the result that the noise due to the material is increased.

For diffuse scattering objects, the noise due to the material is less important than the intermodulation noise which is produced by interference of the individual object partial waves and which in the process of reconstruction preferentially scatters a portion of the signal wave at small angles. The granulation recorded in this way must therefore be kept as small as possible in order to obtain high quality, low noise phase holograms. in order to achieve this, the known photographic bleaching processes have been modified for producing phase holograms. These special bleaching processes, however, are extremely complicated and not usable in practice. In some of the known processes, for example, the developed layer must be treated in more than stages. Other of these known processes result in phase holograms which are not sufficiently stable to light, with the result that the image brightness of the holograms produced diminishes in the course of storage.

in these known processes, the photographic material is fixed after development, and the silver salt produced in the bleaching process is used for constructing the phase hologram. Alternatively, the residual silver halide remaining after development of the silver halide emulsion layer may be used for producing a phase holo- LII gram. In that case, thephotographic material is not fixed after exposure and development. The image silver is converted by a conventional bleaching process into a silver salt which is more readily soluble than silver halides and therefore can be dissolved out of the layer more easily. The resulting reversal of the image does not adversely affect the holographic process since it only causes a phase shift by half a grid period which is insignificant for the purposes of reconstruction. In the known reversal processes of this kind, a strongly tanning developer of the pyrocatechol type is used for development of the exposed silver halide emulsion layer.

Gelatin reliefs are obtained which are distinct only for the low localized frequencies which cause the intermodulation noise. The reversal process effects partial compensation of these gelatin reliefs by phase opposition so that the scattering light is reduced. But even this process is only of limited practical use because the tanning developers are very corrosive substances and therefore physiologically harmful. Moreover, the contrast of phase holograms obtained in this way is relatively low.

It is an object of this invention to provide a simple photographic process of producing phase holograms with high light intensity, high contrast and low noise.

A photographic process for producing phase holograms in silver halide emulsion layers by exposing the light sensitive silver halide emulsion layer to light reflected from the hologram structure, developing the exposed layer, treating it with a short stop bath and washing it, bleaching the silver image by treatment with an oxidizing bleaching bath, dissolving out the silver compound produced by the bleaching process in the exposed areas of the layer and drying the layer has now been found in which a nomtanning developer is used for developing the exposed silver halide emulsion layer.

The process according to the invention results in phase holograms of high light intensity and low noise .which are stable-to light. The holograms obtained by held in the art that the interfering intermodulation noise, known in English language literature as flare light, could only be eliminated by producing a relief structure in the course of development of the exposed layer. It is for this reason that in the known processes development was carried out using a very powerful tanning developer which, however, has the disadvantages indicated above.

The process according to the invention also has procedural advantages in that in the known processes a special bath was always required at the end of the process in order to remove patches which were due to the tanning development. This is unnecessary in the process according to the invention, and the number of process steps required is therefore reduced. In detail, the process according to the invention is carried out as follows:

The hologram is first' produced in the usual manner by interference of the information carrying beam with a reference beam in the photographic layer. The layer is then developed in a conventional alkaline development bath in which the developers used are nontanning developer substances, in particular hydroquinone, l-phenyl-pyrazolidone-3, p-aminophenol or derivatives thereof.

The photographic materialis then not fixed but is treated in a short stop bath of known composition, generally a slightly acid aqueous bath such as dilute acetic acid solution, and is then washed. Thereafter, the silver image is bleached in an oxidizing bleaching bath, preferably an acid bath containing potassium dichromate as oxidizing agent. The bleaching process oxidizes the silver image and converts it into silver compounds, e.g.

silverchromates, which are to a large extent dissolved out by the bleaching bath itself.

After bleaching, the material is washed and then, if necessary, treated with a clarifying bath to dissolve out any residues of silver compound formed in the bleaching process. The clarifying baths used may be slightly alkaline aqueous solutions of sodium sulphite which do not wash-out the residual silver halide from the unexposed areas of the layer.

The layer is then again washed. It is then dried by bathing in alcohol, preferably in ethyl alcohol. The alcoholic bath also contains a desensitizer to eliminate the sensitivity to light of the residual silver halide still present. Suitable densitizers are e.g. Wursters blue perchlorate, phenosafranin, Pinakryptol yellow, Pinakryptol green or Pinawhite.

The preferred desensitizer is phenosafranine. After the treatment in this bath, it is advisable to rinse the layer briefly with ethyl alcohol.

The last mentioned bath desensitizes the residual silver halide and effects uniform and rapid drying of the layer, which is particularly important for producing low noise holograms.

The desensitization and drying with alcohol may, of course, be carried out in separate baths but the combination of the two stages of the treatment in one bath is preferable for the purpose, of simplifying the process.

The process according to the invention may be carried out with silver halide gelatin layers known per se. It is preferred to use fine grained silver halide gelatin emulsions with a particle size of between 20 and 100 nm. The thickness of the layers should preferably be to 30 um.

The quality of the phase hologram is assessed by determining the diffraction efficiency, i.e. the ratio of an intensity diffracted in the first order to the reconstructing intensity, the material noise and the signal noise members for a given test object. The diffraction efficiency of phase holograms obtained by the process according to the invention is about 40 percent. This is of about the same order as that of phase holograms obtained by known processes using tanning development. The figures for the noise power due to the material are on an average less by a factor of 2 to 3 than those obtained with the 'corresponding process using tanning development. The signal/noise ratios for a diffuse object (narrow black line with a width of about 2 mm on a frosted glass screen) with an average localized frequency of about 1600 mm are about 30:]. In the known process in which development is carried out with a tanning developer, the corresponding value is about :1, which means that the signal noises are reduced by a factor of 1.5 in the process according to the invention. Due to the reduced material noise and greatly reduced signal noise numbers, phase holograms are obtained for a reference-object beam ratio of 4:1 with previously unattainable high contrast.

EXAMPLE in a developer of the 65 3.5 g of hydroquinone 30.0 g of sodium carbonate 3.0 g of potassium bromide made up to 1,000 ml with water.

The development time is 5 minutes, the development temperature 20C.

The layer is then treated as follows: Short stop bath:

2 percent aqueous acetic acid solution. Treatment time 2 minutes. Washing:

5 minutes. Bleaching:

In a bleaching bath of the following composition:

5 g of potassium dichromate, 5 ml of concentrated sulphuric acid, made up to 1 litre with water. The bleaching time is 2 minutes. Washing:

5 minutes. Treatment with a clarifying bath of the following composition: 50 g of anhydrous sodium sulphite l g of sodium hydroxide, made up to 1 litre with water. The treatment time is 1 minute. Washing:

5 minutes. Drying and desensitization in the following bath:

88 percent of ethyl alcohol, 10 percent of distilled water, 2 percent of glycerol, 10' mol of potassium bromide, 200 mg/l of phenosafranine.

The treatment time is l0 minutes. The layer is rinsed with ethyl alcohol.

Assessment of the image quality yields the following results:

In the photographic material described above, which corresponds to a plate available commercially under the designation Scientia 8E75 of Agfa-Gevaert AG, the efficiency of diffraction obtained with light of wavelength 647 nm and a localized frequency of 1,650

mm is about 45 percent.

The noise due to the material is less by a factor of about 3 than that obtained when in an otherwise similar process a tanning developer with pyrocatechol as developer substance is used.

The signal/noise ratios for the diffuse object described above are in the region of 35: 1. When development is carried out with a tanning developer, this ratio is in the region of 20:1. The average localized frequency for this measurement was 1,600 mm. The reference beam/object beam ratio was 4: l.

The phase hologram obtained has exceptionally high contrast with excellent stability to light. The formation of print out silver could not be observed even after prolonged exposure to daylight.

What we claim is:

l. A process for the production of a phase hologram by exposure of a photographic material which has at least one silver halide emulsion layer by interfering an information carrying beam with a reference beam in a silver halide emulsion layer, developing the exposed silver halide emulsion layer to produce a silver image, treating the developed layer in a short stop bath and LII Wursters blue perchlorate.

3. A process as claimed in claim 1 in which the desensitizer used is phenosafranine.

4. A process as claimed in claim 1 in which the layer is treated after removal of the silver compounds with an alcoholic bath to promote drying.

5. A process as claimed in claim 1 in which the alcoholic bath contains a desensitizer selected from the group consisting of Pinakryptol yellow, Pinakryptol green, Wursters blue perchlorate and phenosafranine. 

2. A process as claimed in claim 1 in which the desensitizer used in Pinakryptol yellow, Pinakryptol green or Wursters blue perchlorate.
 3. A process as claimed in claim 1 in which the desensitizer used is phenosafranine.
 4. A process as claimed in claim 1 in which the layer is treated after removal of the silver compounds with an alcoholic bath to promote drying.
 5. A process as claimed in claim 1 in which the alcoholic bath contains a desensitizer selected from the group consisting of Pinakryptol yellow, Pinakryptol green, Wursters blue perchlorate and phenosafranine. 